A typical MTJ etched by a chemical etching process is found to have sidewall damage, possibly caused by oxygen or other chemicals during the etching process. Pure physical etching processes such as ion beam etching (IBE) can minimize sidewall damage. However, one drawback of the physical etching process is the sidewall re-deposition of material from the bottom electrode and MTJ materials to the MTJ sidewalls. The sidewall re-deposition of the bottom electrode will lead to a shunting path around the MTJ sidewall and then lead to low yield for the MRAM chip.
Several patents teach methods to reduce shunting. These include U.S. Pat. No. 9,257,638 (Tan et al), U.S. Pat. No. 7,043,823 (Childress et al), U.S. Pat. No. 8,981,507 (Takahashi et al), U.S. Pat. No. 6,798,626 (Hayashi et al), U.S. Pat. No. 8,045,299 (Fontana, Jr et al), U.S. Pat. No. 8,673,654 (Hong et al) and U.S. Patent Application 2016/0079308 (Ito). U.S. Pat. No. 8,045,299 (Fontana, Jr et al—HGST) teaches etching and then oxidizing the MTJ stack or adding ozone or water to the etching process to oxidize the re-depositing material.